Mystery Mortar: 10-inch Seacoast Mortar Model 1840

The 10-inch Seacoast Mortar Model 1840 has always been somewhat a mystery to me.  Diagrams appearing in pre-war manuals don’t match either wartime photos or surviving weapons on display.  And this isn’t just a case of minor variations.

Like many mortar types and calibers, the early American army inherited a quantity of 10-inch mortars from colonial times (as attested to the number of surviving bronze and iron piece around the eastern seaboard).  Early in the 19th century, the army purchased a small number of 10-inch mortars cast specifically for duty in coastal fortifications.  One of those survives today at Fort Sumter.

When the Ordnance Boards of the late 1830s considered seacoast weapons, they proposed 10- and 13-inch calibers.  We’ve seen the 13-inch design was only produced as a prototype (with one of the two bored to 12-inch for tests).  Likewise, Columbia Foundry and West Point Foundry produced one 10-inch prototype each under 1839 contracts.  Two years later, both Cyrus Alger and West Point began small series production of approved 10-inch Model 1840.  Each vendor provided five mortars.

As a standardized type, drill manuals mentioned the 10-inch mortars.  The 1851 Instructions for Heavy Artillery detailed the service of the piece as lesson VI.  The manual included a plate comparing the different classes of mortars, showing the variation in exterior patterns.

Coehorn, stone, siege, and seacoast mortars.  The scan from Google Books is a bit light.  But you can see the main details.  Seacoast mortars were larger, with a band around the center.  The square at the center of that band is the “eye” or loop for lifting the mortar.  That loop does not appear on the smaller siege mortar.  Here’s a retouched line diagram from the 1850 Ordnance Manual:

According to that manual, the 10-inch heavy or seacoast mortar weighed 5,775 pounds.  The overall length of the mortar was 46 inches.  Those dimensions remained the same in the 1861 version of the Ordnance Manual (which also introduced the Model 1861 of the same type and caliber).  However, the listing indicates the model year as 1844, vice 1840.  Since just a few pages later the manual provides particulars in a table titled “Mortars of Model 1841”, the designation is far from concrete.

Even if we settle for Model 1840, there’s still more confusion about the 10-inch seacoast mortar.  Numerous wartime photos show the type in service.  The most famous shows two mortars being emplaced at Dutch Gap.

This is a very interesting photos from several perspectives, which I’ll break out in detail in another post.  For today, let me simply point out these two were cast by Cyrus Alger in 1861 as part of a batch of five produced early in the war. These are positively identified as seacoast mortars by both weight (5800 pounds) and the presence of the lifting loop.

Other 10-inch seacoast mortars appear in a photo from an unknown position on Morris Island. (UPDATE: I tentatively identify this as Battery Kirby on Morris Island.)

See the difference between the line drawing from the manuals and these photos?  No band around the center and no tapering chase.  This may be my “eye” reading too much into the line drawing, but it appears there were subtle deviations from the established pattern.

Another photo comes from the ruins of Fort Pulaski.

This was one of three 10-inch mortars in the Confederate garrison.  The lifting loop is buried, but the exterior form matches those in the earlier photos.  And if you weigh out the possibilities of the mortars origin, there are two leading candidates.  This may be one of the ten produced in the early 1840s.  Or it could be one produced by Tredegar for pre-war and early war orders.  Regardless of the origin, the mortar conforms to a pattern not seen in the official diagrams.

Five 10-inch Model 1840 Seacoast mortars survive today.  Four of those five stand at the Civil War Memorial in Binghamton, New York.  And those mortars match the pattern seen in the photos.  The four Binghamton mortars are from a batch of 18 produced by West Point Foundry in 1861-2.  One other survivor, at Watervliet Arsenal, New York, is also from West Point, but is registry number 2 from the 1840s.

So I question if, before the Model 1861, there was one pattern of 10-inch seacoast mortar or two.  And if there was only one, as clearly seen in the wartime photos and the survivors, were the manuals in error?

I’ll have to journey up to Binghamton secure provide “walk-around” photos.  But for now let me offer up a very well done reproduction, from South Bend Replicas, on display at Fort McAllister, Georgia.

Ft McAllister 5 May 10 091

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Aside from on site notes and links provided above, sources consulted for this post were:

Ordnance Manual for Use of the Officers of the United States Army.  Philadelphia: J.B. Lippincott, 1862. (Google Books copy)

Olmstead, Edwin, Wayne E. Stark, and Spencer C. Tucker. The Big Guns: Civil War Siege, Seacoast and Naval Cannon. Alexandria Bay, NY: Museum Restoration Service, 1997.

Ripley, Warren. Artillery and Ammunition of the Civil War, 4th Edition. Charleston, S.C.: The Battery Press, 1984.

Published by Craig Swain

"Historical marker hunter" and Civil War enthusiast.

6 thoughts on “Mystery Mortar: 10-inch Seacoast Mortar Model 1840

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